Abstract
Numerical response analysis was made using various kinds of vibrational systems with degrading restoring force characteristics and the collapse conditions for those systems were evaluated in connection with the responses of the elastic-perfectly plastic systems. In multi-storied structures the degradation of strength in a story results in concentration of destructive energy into the story and when the decrease of strength reaches a certain value, the degraded story can collapse. Degrading ratio was defined as the ratio of the decrease of horizontal resistant force to the initial yield strength in a specific story. Proposed collapse criterion was expressed in a form of the critical value of the degrading ratio. It is important to note that in the multi-storied structure a little amount of decrease of strength in a story promotes concentration of energy and can cause the collapse of the entire structure.
